Stalker: Call of Pripyat → The Missing Guard and One Shot
As you pass Garik, he'll tell you about the mercenaries he led to Pripyat and how they wanted to kill him. Go to Kovalsky, tell him about the mercenaries, and all the information you've obtained so far. Now we have two options:
1) Eliminate the mercenary leader, which will disorganize them and stop being a problem.
2) Eliminate both the customer and the mercenaries. Krilov takes us to the point, where we're given SVDs and ammo, although I preferred using a Gauss rifle. Wait until everyone has gathered in front of the entrance. The main targets are the mercenary leader "Jackal" and the customer "Serbin" in an environmental suit.
The Missing Sentry
We have a marker on the map indicating where we need to go, so we head for the grocery store. Before we even get there, we hear screams and gunshots. A guard is shooting at someone. We approach him, and in a panic, he kills himself. A few seconds later, we discover the reason—the controller has taken control of him. We kill the controller and contact Kovalsky via radio.
Go to the corpses, search Serbin, and take the Red Keycard to Laboratory X8. After that, return to Kowalski and report the situation. We head to Laboratory X-8.
See also:
Call of Pripyat: Quest "Duty Warehouse"